Recently, there is increasing interest in energy storage technology. Batteries have been widely used as energy sources in portable phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development for them. In this regard, electrochemical devices are subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention.
Among the currently available secondary batteries, lithium secondary batteries, developed in the early 1990's, have a drive voltage and energy density higher than those of conventional batteries using aqueous electrolytes (such as Ni-MH batteries, Ni—Cd batteries and H2SO4—Pb batteries). Lithium secondary batteries have been spotlighted due to the above-mentioned advantages. In general, a lithium secondary battery is manufactured by forming an assembly of an anode, a cathode, and a separator interposed between both electrodes. In the above assembly, the separator interposed between both electrodes of the battery is a member that serves to prevent an internal short circuit caused by direct contact between the cathode and anode. Also, the separator serves as an ion flow path in the battery, and contributes to the improvement of battery safety.
However, conventional batteries, manufactured in the same manner as described above by using a polyolefin-based separator, frequently cause the problems of poor adhesion and separation between a separator and electrodes, and inefficient lithium ion transfer through the pores of the separator, resulting in degradation in the quality of a battery. Additionally, conventional separators are formed from a chemically stable material, which is not decomposed and does not allow any reaction upon exposure to the oxidative or reductive atmosphere inside a battery, such as polyolefin or fluoropolymer. However, such materials provide insufficient mechanical strength, and thus cause the problems of peel-off or breakage of a separator during the assemblage of a battery, resulting in a drop in the battery safety, caused by an internal short circuit of the battery. Further, conventional separators are coated with inorganic particles in order to improve the heat resistance and to provide a high dielectric constant. However, due to the poor binding force between the separator and inorganic particles, the particles are detached from the separator, and thus it is not possible to obtain desired effects.